1. Field of the Invention
The present invention relates to a deaerator, a liquid ejecting device, and an inkjet recording apparatus, and more specifically to a technology for eliminating air bubbles from a liquid, by removing gas from a liquid containing dissolved gas such as ink used in an inkjet printer.
2. Description of the Related Art
In recent years, inkjet printers have come to be used widely as data output apparatuses for outputting images, documents, or the like. An inkjet printer forms data on recording paper by driving recording elements (nozzles) of a recording head in accordance with data, thereby causing ink to be ejected from the nozzles. Ejecting devices for causing ejection of the ink include devices using PZT actuators (piezoelectric elements), or the like, which apply a pressure wave to a pressure chamber connected to a nozzle, and devices using a heat source which heats ink contained in an ink chamber (pressure chamber) and thereby generates bubbles in the ink. Ink pressurized by operating ejecting devices of this kind is ejected from the nozzles and data, such as an image, is formed on a recording medium.
In an inkjet printer, if air bubbles become mixed into the ink inside the recording head, then they can cause ejection abnormalities. For example, in a system using PZT actuators to drive the recording elements, if air bubbles become mixed into the pressure chambers where the ejection energy is generated, then the pressure applied to the ink inside the pressure chambers by the PZT actuators declines and it becomes impossible to eject ink of the prescribed quantity.
Moreover, in a system using a heat source to generate a bubble by heating the ink inside the ink chambers (pressure chambers), air bubbles can affect the amount of ink ejected, the direction of ejection, the speed of ejection, and the like, and as a result, variations in the ejection performance occur.
The ejection abnormalities and variations in ejection performance described above cause deterioration in the quality of the recorded image. Therefore, it is desirable that as little gas as possible is dissolved in the ink that is supplied to the recording head, and hence a deaerating mechanism (deaerator) is used in order to remove the dissolved gas from the ink.
In one example of a deaerating mechanism, a configuration is adopted in which dissolved gas is removed from ink by passing the ink through a porous hollow fiber filter and reducing the pressure in the space surrounding the hollow fiber filter.
In the resin supply apparatus disclosed in Japanese Patent Application Publication No.
8-207048, a first chamber and a second chamber divided by a shutter are arranged between the pellet input opening and the ejection outlet of a plastic extrusion molding device. By controlling the shutter, the first chamber and the second chamber can be connected or hermetically sealed, freely.
Furthermore, Japanese Patent Application Publication No. 2002-307706 discloses an apparatus and a method for replenishing ink into an ink container, which is provided with an ink tank for accumulating deaerated ink and two circulatory paths comprising a deaerating unit. The deaerating units are arranged in the circulatory paths and if the amount of gas contained in the ink is equal to or less than a prescribed value, then the flow path is changed.
However, there is a difference in the frequency of ink consumption (the amount of ink consumed per unit time) in a case where an image is printed and a case where a document is printed. In the case of low-duty operation, namely, intermittent printing such as document printing, the ink is held inside the deaerator for a sufficiently long period of time and therefore suitable deaeration can be performed. On the other hand, in the case of high-duty operation, namely, continuous printing such as image printing, a large amount of ink is consumed per unit time and the time that the ink is held in the deaerator becomes shorter, so that deaeration may not be carried out adequately. Conventionally, the deaeration process is hence optimized in accordance with continuous printing (for example, the length of the flow path inside the deaerator is set to a length that suits continuous printing), and the process is not optimized for intermittent printing.
For the reason described above, during low-duty operation, there is a concern that excessive deaeration may be performed, since even ink that is not required is deaerated. If the ink is deaerated more than is necessary, the solvent in the ink declines and the viscosity of the ink may increase.
In the resin supply apparatus disclosed in Japanese Patent Application Publication No. 8-207048, the shutter simply functions as an opening and closing mechanism between the first chamber and second chamber, and the opening or closing of the shutter does not serve to alter the range of deaeration.
Furthermore, in the apparatus and method for replenishing ink in an ink container disclosed in Japanese Patent Application Publication No. 2002-307706, since the amount of ink in the circulatory paths is large, deaeration takes a long time, degradation of the ink component occurs due to deaerating the ink more than necessary, and hence there is a concern regarding excessive deaeration.